A gas turbine has a compressor and a turbine. Blades or vanes are used both in the compressor and in the turbine, with a distinction being made between stationary guide vanes and rotating rotor blades.
Titanium alloys, which have a high strength, a low density and also good corrosion resistance, are used inter alia as the material for the rotor blades. The titanium alloys disadvantageously have a high notch sensitivity and high cracking sensitivity.
The rotor blades in particular are exposed to various wear processes, e.g. wear by friction or by oxidation. Specifically in a steam turbine, drop impingement erosion occurs as a wear process. Droplets of mist form from water in the steam turbine and are captured by the guide vanes, where they accumulate and break off from the outlet edges of the guide vanes as water drops. The water drops have a low absolute velocity, but, on account of the rotation of the rotor blades, they have a high velocity relative to the rotor blades. If the water drops impinge on the rotor blades with their high relative velocity, this leads to the formation of notches on the surface of the rotor blades.
Various methods are available for reducing the drop impingement erosion. A layer which is resistant to drop impingement erosion can be applied to the surface of the rotor blade by thermal spraying. Furthermore, a hard layer can be applied to the surface of the rotor blade by welding. However, the cracking sensitivity of the rotor blades is disadvantageously increased by said methods, particularly at the interfaces between the titanium alloy and the hard layer, as a result of which the service life of the rotor blades is reduced. Furthermore, it is disadvantageous that the layers cannot be reapplied to the rotor blade after damage caused by drop impingement erosion, because said methods require a smooth surface.